A structural perspective on the PP-loop ATP pyrophosphatase family

Derived from an ancient ATP-hydrolyzing Rossmann-like fold protein, members of the PP-loop ATP pyrophosphatase family feature an absolutely conserved P-loop-like "SxGxDS/T" motif used for binding and presenting ATP for substrate adenylylation (AMPylation). Since the first family member was reported more than 20 years ago, numerous representatives catalyzing very diverse reactions have been characterized both functionally and structurally. The availability of more than 100 high quality structures in the protein data bank provides an excellent opportunity to gain structural insights into the generally conserved catalytic mechanism and the uniqueness of the reactions catalyzed by family members. In this work, we conducted a thorough database search for the PP-loop ATP pyrophosphatase family members, resulting in the most comprehensive and up-to-date collection that includes 18 enzyme families. Structure comparison of representative family members allowed us to identify common structure features in the core catalytic domain, as well as four highly variable regions that define the unique chemistry for each enzyme family. The newly identified enzymes, particularly those from pathogens, warrant further research to enlarge the scope of this ever-expanding and highly diverse enzyme superfamily for use in potential bioengineering and biomedical applications.